Carrier type intertoll dialing telephone system



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I. MOLNAR May 8, 1956 CARRIER TYPE INTERTOLL DIALING TELEPHONE SYSTEM 11 Sheets-Sheet 2 Filed Aug. 13. 1951 ATTYS,

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INVENToR. IMRE MOLNAR ATTYS.

, l. MOLNAR May s, 1956 CARRIER TYPE INTERTOLL DIALING TELEPHONE SYSTEM 11 Sheets-Sheet 4 Filed Aug. l5. 1951 l. MOLNAR.

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CARRIER TYPE INTERTOLL DIALING TELEPHONE SYSTEM Filed Aug. 15, 1951 l. MOLNAR May 8, 1956 I1.1 Sheets-Sheet 8 ATTYS l. MOLNAR May 8, 1,956

CARRIER TYPE INTERTOLL DIALING TELEPHONE SYSTEM 11 Sheets-Sheet 9 Filed Aug. l5, 1951 ATTYS.

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May s, 195s 11 Sheets-Sheet l1 Filed Aug. 13, 1951 ATfys United States Patent 0 l2,l44`,9i5 CARRIER .frYrE iN'rERToLL .DIALING TELEPHONE SYSTEM Imre Molnar, yChicago, lll., as'sgnorgto Automatic Elecitric Laboratories, fln'c., Chica'g'oyr-lll., 1a lcorporation of Delaware Original application July4 10,.'1'947,`1SerialrNo. 760,136,

uowjratem No. 2,603,717, Ydated VA:ply is, ,1952. Divided and -this"application August 13, 1951,"S'e'lfialNm 2'41j505 n zo claims. (Cl. 179-27) TheJpresent inventionrelates to telephone-systems Iand more `particularly to4 such: systems 'of the .intertoll dialing type employing carrier links. This applicationis -a divi-sion -of the copending-application oflmre Molnar, `Se rial No. 760,136, iledluly l0, 1947, .now Patent No. 2,603,717ngranted I ul-y :125, 1952.

Itis a; general object of fthe invention-to:provide'an intertoll dialing system involving -a-vtnetworkiof 4automatic exchanges -and -otiices, provided with tsubscriiber substations, paystations, Amanual Adialkswitchboards and vautomatic dial switchboards,'whereby the .usual trunk and toll connections may be -set up and supervised employinglthe carrier links. v

Another object of the invention is to provide ina telephone system fincluding a remotefexchange yof the :automatic-type, atandem Aexchange of the automaticftype, and a main oice provided with fa switchboard, fan-improved arrangement .forsetting `up connections 'involving -the stations in Ythe exchanges and the switchboard in v the oflice.

-Another -object of'thefinvention :is tolp'rovidein la'tele- .j phone system of the Acharacter-described,vanzirnprovedearrangement for `setting up connections involving thefstations in the exchanges and the switchboard in ytheoflice that `comprise first carrier tlinks between Vfthe y'earchanges and second -carrier =links. between ,the tandem exchange andthe main oice, wherebyffullfandcompletesllpervision of Lthe .connections involving -the :switchboard''attheoftce is -retainedthereby.

2A yfurther object of -the finvention is -.to provide in -a telephone system iincluding -two oices interconnected by a lcarrier -link each provided swith :stations :and fa tswitch board and automatic switching .apparatus, -an improved arrangement `forgpermittingifa switchboard in one=oce t'o control-,over the carrier flink the switching -apparatus in the tother ofce, wherebyconnections may :be textended from Athe .switchboard .inzthe one oceeselectively to ithe l stations and ,to :the switchboard in the v.other .otlce.

-A `furtherrobjectiof thetinvention-isto providefinaartelephone system including 'a ;rstv-oce spovided with manualidial.switchboardiandaafseeond-oceprovidedwith an :automatic -dial switchboard, -an improved .arrangement matic V:switching vapparatus from the `manual fdial-fswitchboard -to :the automatic vdial switchboard, 'whereby sa `delay-:infdal signal is .transmitted .-from theswitchinguapparatus sover= the ecarrier `lilik -to l`thefmanual Vdial switchboard.

55 for setting up `.a connectlonover :a carrierllrnk i and auto- 2,744,965 Patented May 8, .1956

fice

. 2 over the 'carrier link to'the register-sender in order 'to check the sending 'operation thereof in "the event 'the switching apparatus requires a time interval to complete an operation after' receiving'a given digit.

'further 'object of 'theinvention is to provide in a telephone system including l'tv'v'o 'oces interconnected by a toll link, an improved 'arrangement for setting up a connection from a rst switchboard i'n one yof *the o'icesto a secondk switchboard inthe 'other 'of lthe loiices 'via' the carrier link, 'wherein 'allfof the 'different supervisory sign'als 'are transmitted 'over"th'e"`ca`rrier "link betwcnth'e' two switchboards'tnat are necessary Lto facilitate 'die 'handling of toll traffic.

Further featuresrof the invention pertainto'theparticular arrangement 'of 'th'e circuit 'elements 'of the sy's'te'm, whereby the'above-'outlin'e'd and additional perafingfeatures thereof are attained.

4The invention, b'oth as to its organization and method of operation, together 'with further object and advantages thereof, will best be understood 'by reference 'to the following specification 'taken Ai'n 'connection 'with the accompanyi'ng drawings in -'which Figure l is 'a 'diagrammatic illustration of an 'automatic telephone system 'embodying the present invention 'and comprising a remote 'exchange 10,1a 'tandem :exchange '20,away station b$0, amain lofii'ce 46 and a 'distant .office Sil; Pigs. 2 'to l0, inclusive, taken together, illustrate the details of the apparatus incorporated in Vthe 'automatic 'telephone system illustrated in Fig. 1 and 'embodying'the 'features of 'th'e invention'as brie'y outlined above; "and Fig. 1`l is 'a 'skeleton diagram of "the v'sender control circuit that is associated with 'the Strowger dial toll l'board Zin the distant oice 50. Figs. 2`to zl0, inclusive, should be arranged Vfrom leftto 'right in end-mend relation in orderto forma unied'diagram. yMore particularly, Figs. 2 'and 3 illustrate diagrammatically "the .automatic 'switching apparatus vand on'e of the 'pieces 'of carriere'quipment disposed in the lrem'ote'eX- change lil, as wcllas the details 'of one of 'the till'nk 'circuits disposed therein; Figs 4, Sand '6 illustrate diagrammatically the 'automatic 'switching apparatus and one 'of the 'piecesof carrier equipment disposed in the `tanden-rexchange 20,"as well asthe details 'of two di'ie'ren'ttrunk circuits disposed therein; Fig. 6 'also illustrates diagrammatically "one of 'the pieces of carrier current 'equipment disposed 'at'the way 'station 3'0, "as well as -the 'detail's of one of 1'the trunk circuits and one of the alarm 'senders disposed 'th'ereatg Fig. 7 l"illustrates diagrammatically one of the pieces 'of Vcarri'er equipment'disposed at the mainloffce 40, aswell as the details of one 'of Ythe 'trunk circuits, one of the alarm receivers, 'and one of the .cord circuits disposed therein; Fig. '8 illustrates diagrammatically 'the automatic switching apparatus and 'one 'of the 4pieces 'of carrier equipment Idisposed in the vmain oflice 4'0, as 'well as 'the'details of a `'ditler'entone of the trunk circuits disposed "therein; lFigs. 9 'and TO illustrate 'diagrammatically the automatic switching apparatus'and one of vthe vpieces of carrier equipment`disposed in the 'distant oliice 50, as well as "the-details ofone of the trunk circuits vdis'p'os'ed therein; and Fig. '11 illustrates `in skeleton outline certain of 'the relays incorporated in the sender control circuit mentioned. r

VThe automatic `tf'slephone system Referring 'nowinore particularly to Fig. l, the automatic telephone system there yillustrated comprises .the remote 'exchange 10 'serving a number of ordinary .subscriber subs'tation's, including the subscriber substation T11, anda number of paystations, including the paystation T12. v'l`he's'lbscriber substation T11 is provided with a 4subscriber 'line 211-extending thereto and having a line circuit Z13V individually associated therewith; and thepa-ystation T12 is provide'dwiih alin'e 212 extending thereto and having 'a line circuit 212i vindividually associated therewith. Also the remote exchange comprises a plurality of groups of finder-selector links, the rst group including the nder-selector link 203 and provided with a distributor 204; as well as a plurality of groups of local connectors, the iirst group of local connectors including the local connector 205. Preferably, the subscriber line 211 extending to the subscriber substation T11 and the line 212 extending to the paystation T12 are arranged in the tirst group of lines and are accordingly accessible both to the finders of the irst group of finder-selector links 203, etc., and to the irst group of local connectors 205, etc. Further, the remote exchange 10 comprises a group of incoming selectors, including the incoming selector 206, having access to the diierent groups of local connectors; the local connector 205 in the first group being accessible to the incoming selector 206 via the trunk 207 extending thereto.

The remote exchange 10 and the tandem exchange 20 are interconnected by a plurality of channels of carrier equipment; the first channel illustrated including the line 60 extending between the remote exchange 10 and the tandem exchange 20 and respectively terminating in the carrier equipment 394 provided in the remote exchange 10 and in the carrier equipment 494 provided in the tandem exchange 20. The carrier equipment 394 is'connected to a trunk circuit 200 individual thereto provided in the remote exchange 10; which trunk circuit 200 is connected by a trunk 230 to the incoming selector 206 individual thereto. Also the trunk circuit 200 comprises two additional trunks 220 and 225, both accessible to the selectors of the diiferent groups of finder-selector links. Finally, the selectors of the different groups of finderselector links in the remote exchange 10 also have access to the diterent groups of local connectors therein. Spcciiically, the selector of the nder-selector link 203 has access to the local connector 205 via the trunk 207 extending thereto.

The tandem exchange 20 serves a number of ordinary subscriber substations, including the subscriber substation T21, and a number of paystations, including the paystation T22. The subscriber substation T21 is provided with a subscriber line 421 extending thereto and having a line circuit 423 individually associated therewith; and the paystation T22 is provided with a line 422 extending thereto and having a line circuit 424 individually associated therewith. Also the tandem exchange 20 comprises a plurality of groups of iinder-selector links, the first group including the finder-selector link 426 and provided with a distributor 425; as well as a plurality of groups of local connectors, the first group of local connectors including the local connector 427. Preferably, the subscriber line 421 extending to the subscriber substation T21 and the line 422 extending to the paystation T22 and arranged in the first group of lines and are accordingly accessible both to the finders of the lirst group of iinder-selector links 426, etc., and to the first group of local connectors 427, etc. Further, the tandem exchange 20 comprises a irst group of incoming selectors, including the incoming selector 429, having access to the different groups of local connectors; and a second group of incoming selectors, including the incoming selector 434, having access to the different groups of local connectors; the local connector 427 in the iirst group being accessible to the incoming selectors 429, etc., and 434, etc., via the trunk 428 extending thereto. The carrier equipment 494 in the tandem exchange 20 is connected to a trunk circuit 400 individual thereto; which trunk circuit 400 is connected by a trunk 435 to the incoming selector 429 individual thereto. Also the trunk circuit 400 comprises an additional trunk 430 accessible to the selectors of the different groups of finder-selector links and to the group of incoming selectors 434, etc.

The tandem exchange 20 and the way station 30 are interconnected by a group of trunk lines, including the trunk line 665. Each of the trunk lines terminates in a trunk circuit provided in the tandem exchange 20 and in a trunk circuit provided at the way station 30; the` trunk line 665 terminating in the trunk circuits 500 and 600 respectively provided in the tandem exchange 20 and at the way station 30. The trunk circuit 500 is connected by a trunk 520 to the incoming selector 434 individual thereto. Also the trunk circuit 500 comprises two additional trunks 510 and 515 respectively accessible to the selectors of the different groups of finder-selector links and to the incoming selectors 429, etc. Finally, the selectors of the diierent groups of finder-selector links in the tandem exchange 20 also have access to the different groups of local connectors therein. Specifically, the selector of the finder-selector link 426 has access to the local connector 427 via the trunk 428 extending thereto.

The way station 30 and the main oiice 40 are interconnected by a plurality of channels of carrier equipment; the rst channel illustrated including the line 70 extending between the way station 30 and the main oice 40 and respectively terminating in the carrier equipment 649 provided at the way station 30 and in the carrier equipment 794 provided in the main oiiice 40. The carrier equipment 694 is connected to the trunk circuit 600 individual thereto at the way station 30; which trunk circuit terminates one end of the trunk line 665 extending between the tandem exchange 20 and the way station 30, as previously noted. Also a plurality of alarm senders 680, etc. are provided at the way station 30 and respectively connected to the carrier equipment 694, etc., thereat.

The carrier equipment 794 provided in the main ofiice 40 is connected to a trunk circuit 700 individual thereto; which trunk circuit 700 terminates in a jack J 730 appearing before an operator switchboard 765 in the main oliice 40; which operator switchboard 765 comprises a plurality of cord circuits, including the cord circuit 766. Also a plurality of alarm receivers 770, etc., are provided in the main office 40 and respectively connected to the carrier equipment 794, etc.

The main oflice 40 serves a number of ordinary subscriber substations including the subcriber substation T41. The subscriber substation T41 is provided with a subscriber` line 841 extending thereto and having a line circuit 842 individually associated therewith. Also the main oice 40 comprises a local switch train 844 provided with a distributor 843. The subscriber line 841 extending to the subscriber substation T41 has access to and is accessible to the local switch train 844. Also the main ofiice 40 comprises a group of C. L. R. trunks including the C. L. R. trunk 846. The C. L. R. trunk 846 is accessible to the local switch train 844 via a trunk 845 extending thereto and is also provided with a trunk 847 extending therefrom which terminates in a jack 1848 appearing before the operator switchboard 765.` Moreover the main oli-ice 40 comprises a tool switch train 805 having access to the lines 841, etc., respectively extending to the subscriber substations T41, etc.; which toll switch train 805 has a trunk 806 extending thereto and terminating in a jack J 807 appearing before the operator switchboard 765. Further, the main oflice 40 comprises a group of incoming selectors, .including the incoming selector 812, having access tio the toll switch train 805 via the trunk 806 extending thereto. Alsov the main otlice 40 comprises a group of toll trunks inward 809, etc. -The toll trunk inward 809 is accessible to the incoming selector 312 via the trunk 808 extending thereto and is provided with a trunk 810 extendingtherefrom and terminating in a jackv 1811 appearing before the operator switchboard 765.

The main oice 40 and the distant office 50 are interconected by a plurality of chanels of carrier equipment, the iirst channel illustrated including the line extending between the main oice-40 and the distant oice 50 and respectively terminating-in the carrier equipment 894 pro vided .inthe mainotfce 40;and.. in...the.-,carrier.:equipmentsi 99.4.providedimthev distantoicesS. The. carrienequiml ment. 89.4 i is connected.topa.` trunk.circuit 800. individual..1 thereto in the mainoiiices40lwhich trunk..circuit;800.is..v

conectedby a trunk. 875 tothe .incoming selector 812 individual thereto. Also.. the trunk. .circuit 8.00.fterminates;. in..a jack 1815. appearing. before the! opeartor, switchboard.;

Tliejdistant office 50S'serves.a. number. offordinary, sub'.-

scriber substations,, inc1uding. the` subscriber: substation.v T51. The.. subscribensubstation T511, isprovidedwith a subscriber. line .10511.extending ,theretoand. having. line. .f. circuit. 1052 .individually associatedltherewithf.. Alsotthezy distant office 50. .comprses=.a. local switchtrairn105.4l `providedwith.a..distribntor-1053... The subscriberline 105.1` extending, to the.subscribersuhstation T51 has access to.

andtisfaccessiblieto the local switchtrain. 1054. y Alsothe..

dividual .to the.. toll operator.. .position 10.61 inc1uding the Iinder-se1ectorlink 10.62.. Morex/over. thetoll board 1060 comprises-a sender control .circuit 20Y.. connected .to the.

operator. position1061a keyset ZZKYI atthe operatorposi.- tionfllfthat is connected'tothe sender. controlcircuit ZOY, and. a register-sender.. 21Y that. is .connected .to a .the

senderhcontrol circuit 20Y`;1the. register-senderZIY con.- sistingofi an .impulse sender. 21AY and .a number. odigitf registers-BY; Further, the distant.oice50-comprisesa.. group of C. L.Y Retrunks,..including, .thef C.. L. R.tr11nlc,-l

1056;.,the C. L. R` trunk .1056 is accessible to the..local switchtrain 1054 viaa.. trunkf1055-extendi1'1g thereto;. which .C..L. R'.-trunk.circuit 105.6 isralso .provided withr .21.

trunk.1057 extending therefrom .thatjs .accessible to the finders. of: the finder-selector links associatedawithlhe.,

varioustollfoperator positions atithe .Strowger dial toll...l

board .1060.f Moreover, ythe'.distantolil'ce Siltcomprisesv a itollswitchtrain 1038.having.access to the`` lines v 1051, etc., respectively extending .to. .the subscriber. substations T51, etc.; which tolli switchftrain. 1038.-has.a tlrunlelil'l extending Lthereto jthatis accessible.. to. the. selectors of. the.V nde'r-selector links associatedwith the various tolloper.- ator positions: at the. Strowger dial tolhboard. 1060-.

Further, the l.distant oilice. 50 'comprises a group. of in-y coming selectors, includingthe incomingselector1036, havingfaccess .to the. toll.switch train. 1038-via.the,. trunk 1037 extendingjhereto. Also thedistantoceySOscome. prises agroupofioll trunks-inward.1066,.etc.. Thetoll;

trunksinward 1066lare accessible to. the .incoming selector..k 1036-jvia Aa trunk 1065.extending.,thereto. and .is provided...

with a trunk. 1067 extending .therefrom and.accessible yto thefinders of the finder-selector links-associatedwith'the various. toll4 operator positions. at. the..,Strowg eri.dialtoil. board.1060`.

The carrier equipment 994provided. inthe. distantoi'ce..

50'iis connected to .the trunk circuit900` individualthereto;

which trunk circuit 900 is .connected via a.trunk. 1030 to v Also the Y trunk circuit 90.01isprovided withla.trunk-.1040..incoming g thev incoming selector. 1036 individual thereto.

thereto that( is. accessibletothe. selectors .of rthe .finder-f selectorlnks. associatedwith the various;.toll operator.. positions vat the. Strowger.. dial tollfboard. 10601..

The apparatus incorporated in vth'eauz.0mall'c telephonesystem Preferably, the carrier system interconnecting. the.. re-.- mote exchange 10 andthe tandem exchange 20,. the,.car.,- rier system interconnecting the .way'station 30. and theV mainoce 40 'and lthe carrier system interconnecting the.

main ,ofiice..40 and the .distant oice. 50 are .identical,and:.. each comprises atype. 32,Lenkurt unit; of thecharacter.

disclosed in .the copendingl.` applicationvof .Imre1=.Molnar,

SerialLN. 728,422;l f`11d,Fbi1uary.-14, 19,47,y now yPatent.. No. 2,559`,l65,lgranted July 3.49.51.. Alternatively. 111e.y

6. carrier.. equipment ,.interconnectingtheivarious-iexehansesa ofces and way stations mentioned maynbefofsthvradiof linlctype disclosedzinsthe...copendingaapplicationOfflmre Molnar, seriaiNo. 746,929,1i1ed 9.4.1947. 'rhus...the.

carrier. equipment .494, .179.4 and .9M-.respectively disposed at vthe east. termini., of the.,lines..f.60,f 70, and.80,. andfrespecfe 'i tively,j comprising ;..portions.. of.. the` rst; channels .y iniI the threel carrier.. current systems :'mentioned, transmitaatrae.

carrier.: frequency of 15,'95 kc.. for:v signalling purposes,

,l purposes. Similarly, .the .carrier equipment 39.4, -.I69,4 and..,

S94 respectively disposed. fat. the,.west.-terminiof .the lines'.`

60, '70 and 80, .and respectively.comprisingportionsoff-the:;

for signalling, purposes, and freceive the 1ov.f er side` bandi.

of the carrier.l frequency. 15.95=.. kc. (13.1.10 Y`15.7-."kc.) fom communicationpurposes.

Also, each carrier. equipment ,39.4,v etc., LIcomprisesan@ outgoing.4 signaltransmitting v.channel inc iudingar first car.- rier` frequencyoscillator anda transmitting,y amplifier pro-., vided with a .plate circuit; -controlledsbyfamassociatedrsig nal-outfrelay; as. well as anzoutgoing.communicationchanf.

nel including a balancedmodulator connected. .tostherstsk carrier-,frequency oscillator and an.v associatedxtransmitting bandpass filter... Also, each fcarrier. .equipmentmentioned-f comprises yan incominggsignalchannel.including a-rectiiier;

anda signal-in relay; `as ,well-.as aniincomingucommunica-.-

tion-channelincluding a balanced demodulator connectedt to la lseeondcarrier..frequencyfoscillator and: an; associated n receivinggband passilten Also-each.1 carrier equipment mentioned vcomprises' a ,transmitting direction {.flten con.`

carrier equipmenttmentioned comprisesza high., pass-t line filter connected.`.between-the. associatedfline terminustfand theA transmitting directionalter, and the vreceiving.direction-zfilter.I Finally.y each line.Y terminus .is connected..1byfalowpass. lter. to .other ,voice frequency equipment. Thiscon: l. ventional. equipment described.abovev and `disclosed infthe-fi previously mentioned copendingMolnar,application, per. mits utilization ofthe 1inesf60, 70 and.S0tinr oth.erf-voiceefrequency` equipmentain-a manner Well understood:

As shown. ini Fig... 2, preferably; each.- .ofvthe.;A finder-- selector links 203, etc'.,. eachofi the:1oca1tconnectors1205,; etc., and each. ofthe incoming selectors 206,-. .etc are off.; the conventional Strowger types; ,whilethey distributor, 204e., andthe line circuits. 213, 214, ..etc.,.areyofranyfsuitable types. Finally, each=of the..subscriberjsubstationsi-T1r1,l etc., is provided. with conventional. substation.apparatus,;,; each subscriber line .211, etc;, is.provided.\with zie-meten, notshown, individual thereto; and each.of..the'.paystations; T12,..etc. is, of thecharacter of that disclosed iindig. 3. of United States .Patent -No. 2,137,409., grantedNovember 22, 193 8,1 .to Talbot G; Martin and, Clarence f Ea.; Lomax Specifically, apaystation ofthis typefcomprises, among;-l

other elements, ,a transmitterbridgedby angasymmet'ricalf. currentfconducting devicein theform'of az. copper. oxide;` rectifier; wherebyapersonat the paystationmayf.controley the extension of, a connection Atherefromy and converse Y with an operatonwithout depositing a coin thereatr Also,

the personvat therpaystation can normally-extenda. con nection therefrom=to-a subscriber substation,-butlcannot;l talk to.. the subscriber-...werent..unti1-,a,.coin,1hasbeenrdef posited anthefpaystation, as. a-.;.cons.eq1 1ence.-oft-.theubloektring., action.- .ofgtheffcoppen oxidez--rectien Iwith@respects tot.

the transmitter when the polarity of theline is reversedy in a local connection.

Preferably, each of the trunk circuits in the remote exchange 10 is identical to the trunk circuit 200 that comprises, as shown in Figs. 2 and 3, a relay group including a timer relay R235, a reverse battery relay R240, a series relay R250, a switch relay R260, a supervisory relay R270, a timer relay R280, an answer relay R310, a dial relay R320, a line relay R330, a hold relay R340, a signal-in relay R350, two digit relays R360 and R370, a hold relay R380 anda tone relay R390. Also, the trunk circuit 200 comprises an impedance 257 and a busy tone transformer 346. At this point it is noted that the trunk circuit 200 is connected to the carrier equipment 394 by a pair of line conductors C301 and C302, a signal-out conductor C303 and a signal-in conductor C304; and that the apparatus provided in the carricr equipment 394, as previously explained, comprises a signal-in relay R395 and a signal-out relay R397.

In the tandem exchange 20, as shown in Fig. 4, each of the finder-selector links 426, etc., each of the local connectors 427, etc., and each of the incoming selectors 429, etc., and 434, etc., are of the conventional Strowger types; while the distributor 425 and the line circuits 423, 424, etc., are of any suitable types. Finally, each of the subscriber substations T21, etc., is provided with conventional substation apparatus; each of the subscriber lines 421, etc., is provided with a meter, not shown, individual thereto; and each of the paystations T22, etc., is of the character of that disclosed in Fig. 3 of the previously mentioned Martin et al. patent.

In the tandem exchange 20, preferably each of the trunk circuits in the group, including the trunk circuit 400, isidentical thereto; which trunk circuit 400 comprises,

as shown in Fig. 4, a relay group including a supervisory relay R440, an answer relay R445, a signal-in relay R450, a dial relay R455, a switch relay R460, a line relay R470, a hold relay R480, a control relay R490, and a hold relay R400, as well as an impedance 458. At this point it is'noted that the trunk circuit 400 is connected to the carrier equipment 494 by a pair of line conductors C401 and C402, a signal-out conductor C403 and a signal-in conductor C404; and that the apparatus provided in the carrier equipment 494, as previously explained, comprises a signal-in relay R495 and a signal-out relay R497.

Also, in the tandem exchange 20, preferably, each of the trunk circuits in the group, including the trunk circuit 500, is identical thereto; which trunk circuit 500 comprises, as shown in Figs. 5 and 6, a relay group including a reverse battery relay R530, two timer relays R540 and R550, a supervisory relay R560, a tone relay R565, a hold relay R570, a supervisory relay R580, a seize relay R585, a control relay R590, an answer relay R595, a line relay R610, a pulse relay R620, a switch relay R630, and a dial relay R640. Also, the trunk circuit 500 comprises an ordinary battery indicated, a booster isnoted that the trunk circuit 600 is connected to the carrier equipment 694 byva pair of line conductors C601 and C602, a signal-out conductor C603 and va signal-in conductor C604; and that the apparatus provided in the carrier equipment 694, as previously explained, comprises a signal-in relay R695 and a signal-out relay R697.

Preferably, in the way station 30, each of the alarm senders is identical to the alarm sender 680 which comprises, as shown in Fig. 6, a motor 681 operative from a commercial source of single phase A. C. power and operatively associated with a set of switchspringsS682 and witha gearbox 683.- The gearbox 683is adapted to 8 v t time operation of the motor 681 and at theexpiration of ten minutes to open the associated contacts S684 and to close the associated contacts S685. Further, the alarm sender 680 comprises a start relay R686.

In the main oice .40, preferably each of the trunk circuits in the group, including the trunk circuit 700, is identical thereto; which trunk circuit 700, as shown in Fig. 7, terminates in the jack 1730 before the operator switchboard 765, as previously noted, and comprises a relay group including a signal-in relay R705, a jack relay R710, and a sleeve relay R720. Also, the trunk circuit 700 comprises a busy lamp L732 and a line lamp'L733 disposed at the operator switchboard 765. At this point it is noted that the trunk circuit 700 is conectedto the carrier equipment 794 by a pair of line conductors C701 and C702, a signal-out conductor C703 and a vsignal-in conductor C704; and that the apparatus provided in the carrier equipment 794, as previously explained, comprises a signal-in relay R795 and a signal-outrelay R797.

Preferably, each of the cord circuits 'disposed at the operator switchboard 765 is identicalto the cord circuit 766 which, as shown in Fig. 7, terminates into front and rear plugs P748 and P758, respectively, and comprises a dial D760, a dial key K737, a ring key K736, a talk front key K734 and a talk rear key K735. Also, the cord circuit 766 comprises a front supervisory lamp L747, a rear supervisory lamp L757 and a relay group including a dial front relay R740, a supervisory front relay R745, a dial rear relay R750 and a supervisory rear relay R755. Finally, it is noted that the cord circuit 766 is associated with a headset 767 disposed at the operator switchboard 765 and with an interrupted generator 738.

Preferably, in the main oice 40, each of the alarm receivers is identical to the alarm receiver 770 which comprises, as shown in Fig. 7, a motor 773 operative from a commercial source of single phase A. C. power and operatively associated with two sets of switch springs S777 and S778 and with a gearbox 774. The gearbox 774 is adapted to time operation of the motor 773 and at the expiration of 9% minutes to close the associated contacts S775 and at the expiration of lOl/ minutes to close the associated contacts S776. Further, the alarm receiver 770 comprises a relay group including an alarm relay R780, a start relay R785, a hold relay R790 and a timer relay R700. Finally, the alarm sender 700 comprises an alarm lamp L771, a delayed alarm DA772 and a reset key K773.

In the main office 40, preferably each of the trunk circuits inthe group, including the trunk circuit 800, is identical thereto; which trunk circuit 800 terminates in the jack 1815 before the operator switchboard 765, as previously noted and comprises a relay group including a sleeve relay R820, a signal-out relay R830, a jack relay R835, a hold relay R850, a dial relay R855, a signal-in relay R860, two re-ring relays R865 and R870, a switch relay R830 and an answer relay R890. Also, the trunk circuit 800 comprises a repeating coil RC875, as Well as a busy lamp 1.817 disposed at the operator switchboard 765. At this'point it is noted that the trunk circuit 800 is conected to the carrier equipment 894 by a pair of line conductors C801 and C802, a signal-out conductor C803 and a signal-in conductor C804; and that the apparatus provided in the carrier equipment l894, as previously explained, comprises a signal-in relay R895 and a signal-out relay R897.

In the main oliice 40, as shown in Fig. 8, preferably the local switch train 844, the ytoll switch train 805 and the incoming selectors 812, etc., are of the conventional Strowger types; While the distribtuor 843, the line cir- -cuits 842, etc., the C. L. R. trunks 846, etc., and the toll prises,as shown in Figs. 9 and 1-0, a relay group including aai-agees a signal-in relay.R920, a hold ,relay R930, .a.dial.relay R940, a `trouble relay R950, a seizere'layRQSS, .a'swith relay R960, a re-ring relay .R970 and-an end-of-.dil relay R980, an answer relay R975, a line relay R1'010, 'a trouble relay R1020 andare-ring relay'R1025. Also, the trunk circuit 900 comprises a repeating coil RC910. At'this point, it is noted that the trunk circuit"900 isconnected to the carrier equipment`994 by a,pair of lineconductors`C901 and C902, a signal-out conductorC903 and a signal-in conductor C904; and that the apparatus provided inthe carrier equipment 994, as previously explained, comprises a signal-'in relay R995 and a signalout relay R997.

-In the distant office 50, asshownin Fig. preferabl-y the local switch train 1054,'thetoll switchtrain1038, 'the incoming selectors 1036,.etc., and theiinder-selectorilinks 1062, etc., Yare of the conventional Strowger-types; while the distributor 1053, 'the vline circuits 1052, etc., the C. L. R. Vtrunks 1056, etc., and the toll trunks inward 1066, etc., are of any suitable types. Further theStrowger dial toll'board 1060 is Vof the connection and arrangement of that ydisclosed inU. S. Patent No. 2,353,212 "granted July 11, 1944, to Harvey W. Balzer;.and in the present arrangement the reference characters Y,21Y, etc.,'designate pieces of apparatus 'that are identical to the-.corresponding pieces of apparatus designedby .the reference characters 20, 21, etc., and disclosed in detail in the Balzer patent. For example, as illustrated in Fig. 11 herein, the sender control circuit` 20Y includes, among Otlrerrelays, the relays R3520Y, R3530Y and R3540Y that correspond respectively .to the relays R3520, 123530 and R3540 -in the sender control circuit '20 shown in Figs. '34, 35, 36 and 37 of the Balzer patent. Finally, each of the subscriber substations T51, etc., is provided with conventional substation apparatus.

A better understanding of the connection and arrangement vof the apparatus incorporated in the automatic ,telephone system illustratedin Fig. 1 and briefly described above will be facilitated from a consideration rof the extension of connections involving the different exchanges and oices as will appear hereinafter.

Local .calls in heremote exchange `10 First assume that a call initiated-ata subscriber substation such, for example, as `the lsubscriber substation T1-1 in the remote exchange 10 is to bev extendedto 'a'paystation such, for example, as'the paystationTlZftherein. When the call is initiated at the Acalling subscribersubstation T11, the line circuit 213, associated withtthe 'subscriber line 211, operates tojmark the subscriber 'line 211 as busy to the local connectors1205,'etc., having "access thereto, and to initiate operation of the distributor""204. The distributor 204 assigns an idle oneof'the finder-selector links such, for example, as the finder-selector'v link 203 in the iirst group for use at this time; whereby theiinderof the iinder-selector links 203 operatesto `seize ,the subscriber line 211. The subscriber lat Vlthe ycalling subscriber substation T11 then dials the directory number "of-'the called paystation T12, whichmay 'be `112. Thefselector of the nder-selector link 203 `responds to'thefnst digitll to select the iirst group of local connectors, includinrgfthe local connector 205, and then an idle local connector therein. For example, the selectorfof'thenderselector link 203 may select the trunk ,207 extending tothe particular local connector 205; whereupon the local connector 205 is rendered responsive 4`to the next two "digits dialed at the calling subscriber'substation T11. The Ysubscriber at the calling subscriber substation Tlil'then'procee'ds tol dial kthe next two digits 1 and 2; whereby the local connector 205 is operated to seize the.'line 212 extendinggto the called paystation T12; whereupon'the 'idle ',orbusy condition of the line v212 is'tested by thelocal connector 205 at this'tirne. l Y

First assuming `that the called paystation T12 isbusy at this`time, the local connector205 ttests the'lin'ei212extending ,theretov as busy returning "busy tone 'current over the .trunk 20.7., theinderfslector link 203 cthensulr scriberline '211 .to the .calling subscriber substation :Tllin orderto indicate `to .the subscriberthereatthatathe desired connection `may vnotfbe had ,at l:this .time v.due to thebusy condition of the called paystation T12. The lsubscriber at the calling subscriber substation T11 then proceeds to release the Eapparatus in a manner more fully explained hereinafter. l

Now assuming that the called paystation T12 yis-idle at .this `time, :the,1ocal,connector,205 operates to project ringing .current over ntheline 2,12 ,to the .called paystation T12 and Atoreturn .ring-back tonecurrentover the vtrunk 207,and,:consequently, to the callingsubscriber substation FE11 inl-order :to indicate .tothe vsubscriber thereatfthat'the called .paystation T.12.is being rung. When aperson at the called paystation Ianswers the fca11,'the `local connector .265 operates inforderto revcrsethe polarity of the trunk .207; whereby the .nder=selector link203 operates \tl1e.n1eter,-not shown, associated 'with the fsubscriberline 21.1.in orderto meterthe callin a conventional manner. At'this time, an-established connection -is completed .between .the A,calling subscriber substation Till yand the -;.called paystation T12 and conversation l therebetween then proceeds in the usual manner. v

At the conclusion of the established-connection, `when the person .at thepaystation .T12y disconnects, the local connector 205 again operates to Vreverse the polarity of the trunk .207; however, .withouteifect at4 this time. Subsequently, when the subscriber 'at the'calling'subscriberlsubstation T11:disconnects, the loop, circuit extending to fthe local connector 205 is interrupted vin order to cause'the local :connector 205 and-the tinderselector link 203-todae released. Whenthe.localconnector-205.is thus released, the line 212 extending to the paystation T12 is again marked as idle-by the associated line circuit 214 tothe local connectors 205, etc., having access thereto. .Simi' larly, when vthe finder-selector link .203 -is vthus released, the line 2111 extending Vtofthe subscribersubstation .T11 is marked as idle vby the vassociated Aline 'circuit Tf'latothef local connectors y205, ctc., having access thereto. Also, when the finder-selector link 2,03tis thusreleased, the trunk 207 extending to the local connector 205 is marked as idle to the iinder-selector links l203,etc., having-access thereto. At this time the established connectionbet-ween thefcalling subscriber -substation Tlland 'the' called paystation T12 is released andall of 'the apparatus involved therein is completely released ,and available vforfurther use.

in yView oftheuforegoingit will be understood thata connection maybe extended yfronifafcalling subscribersubstation T11, `etc., in the `remote yexchange 10 to another called subscriber substation therein Vin an identical manner. Also, it will be understood 4that a connection-from a calling ,paystation T12, etc., -in the remote exchange 10 may be extended to a called subscriber substation T11, etc. .orto another -ca'lledpaystationtherein ina substantiallyridentical manner. In-'thisconjunction, it is 'noted incident to extending -a connection from the calling paystation-.T12 in the remote'exchange =10 `to a` calledsubscriber substationor'to another called paystationftherein, that w-hen'the callis -answered,gthe local connector 205 operates to revcrseithepolarity'ofthe trunk 207 Yand over the finder-selector,linkl'employed and the linet212 to the calling `paystation T12. This reversalof-pola-rity to the calling paystation T1-2lbringsabout-blocking of the transmitter at the calling paystationy T12 by the associated copper oxide; rectiierunless vthefperson -at the paystation T12 has depositedzacoiniat thistime. More-particularly, in vthereventthe person atthe calling paystation T12 has not `deposited a coin I-a'tthistime he may hearlthe person at thecalle'd 'subscriber substation or vat'the calledpaystation inthe-remote exchange 10,"but'he may not talk to the person lmentio'nedby virtue'ofrthe 'circumstance th'at'lthe Ycopper `oxide' rec'tiiier fblocks the associated :transmitter `as a consequence 'of the reversal of polarity 'to the calling paystation T12. However, when the person at the calling paystation T12 deposits a coin, the copper oxide rectifier is removed from blocking the transmitter thereat; whereby the connection is completed in the manner previously explained.

A call from a subscriber substation r paystation in the remote exchange to a subscriber substation or paystaton in the tandem exchange First assume that a call initiated at a subscriber substation such, for example, as the subscriber substation T11 in the remote exchange 10 is to be extended to a subscriber substation such, for example, as the subscriber substation T21 in the tandem exchange 20. When the call is initiated at the calling subscriber substation T11, the line circuit 213 associated with the subscriber line 211 operates to mark the subscriber line 211 as busy to the local connectors 205, etc., having access thereto, and to initiate operation of the distributor 204. The distributor 204 assigns an idle one of the finder-selector links such, for example, as the finder-selector' link 203 in the first group for use at this time; whereby the finder of the finder-selector link 203 operates to seize the subscriber line 211.

The Subscriber at the calling subscriber substation T11 in the remote exchange 10 then dials a prefix digit such, for example, as the prefix digit 9, indicating that the call is to be extended to the tandem exchange 20, followed by the directory number of the called subscriber substation T21 in Ithe tandem exchange 20, which number may be 121. Thus the subscriber at the calling subscriber substation T11 first dials the prefix digit 9; whereby the selector' of the finder-selector link 203 responds to the first digit 9 in order to select the corresponding group of trunks, including the trunk 225, and then an idle `trunk therein. For example, the selector of the finder-selector link 203 may select the particular trunk 225, assuming that the trunk circuit 200 is idle at this time; the trunk 225 being marked as idle to the selector of the finder-selector link 203 by the application of battery potential to the control conductor C223 thereof. More particularly, battery potential is normally applied by way of the impedance 257, the contacts 266 and 383 to the control conductor C223 of the trunk 225.

Also, when the selector of the iinder-selector link 203 seizes the trunk 225, a loop circuit is completed for energizing the upper and lower windings of the line relay R330 in the trunk circuit 200. This loop circuit extends from ground by way of the contacts 362, the lower winding of the line relay R330 and the contacts 244 to the line conductor C227 of the trunk 225; and from battery potential by way of the upper winding of the line relay R330 and the contacts 242 to the line conductor C226 of the trunk 225. When this loop circuit is thus completed, the line relay R330 operates to complete, at the contacts 331, an obvious circuit for operating the hold relay R380. Upon operating the hold relay R380 inter rupts, at the contacts 383, a point in the previously traced path for applying battery potential to the control conductor C223 of the trunk 225; and completes, at the contacts 384, a path including the upper winding of the tone relay F390 for applying ground potential to the control conductor C223 of the trunk 225. When battery potential is thus removed from the control conductor C223 and ground potential is applied thereto, the trunk 22S and, consequently, the trunk circuit 200 is marked as busy to the selectors of the other finder-selector links having access thereto. Also the upper winding of the tone relay R390 is energized causing this relay to operate and complete, at the contacts 391, an obvious path for applying ground potential to the tone start conductor C349, thereby to initiate operation ofthe associated tone apparatus. Also, the hold relay R380 interrupts, at the contacts 381, a normally completed termination circuit also including the contacts 311, the resistor 344, the contacts 281, the condenser 286 and the condensers 347 and 348 across the line conductors C301 and' C302 extending to the carrier equipment 394. Also upon operating the line relay R330 completes, at the contacts 333, an obvious path for applying ground potential to the signal-out conductor C303 extending to the carrier equipment 394 in order to effect operation of the signal-out relay R397 therein. Upon operating the signalout relay R397 in the carrier equipment 394 closes the contacts 398 included in the plate circuit of the associated transmission amplifier; whereby the 24.55 kc. carrier signal from the associated carrier frequency oscillator is transmitted for signalling purposes over the associated line 60 extending between the remote exchange 10 and the tandem exchange 20.

When the 24.55 kc. carrier signal is received in the carrier equipment 494 disposed in the tandem exchange 20, the carrier equipment 494 brings about restoration of the normally operated signal-in relay R495 therein; whereby the latter relay upon restoring closes the contacts 496 applying ground potential to the signal-in conductor C404 in order to effect operation of the signal-in relay R450 in the trunk circuit 400. Upon operating the signal-in relay R450 completes, at the contacts 452, an obvious circuit for operating the hold relay R400; which latter relay upon operating, completes, at the contacts 405, a circuit, including the contacts 485 for energizing the upper winding of the switch relay R460 in order to cause the latter relay to operate. Upon operating, the switch relay R460 interrupts, at the contacts 466,

` a normally completed path including the impedance 458 and the contacts 483 `tor applying battery potential to the control conductor C433 of the trunk 430; and completes, at the contacts 467, a path including the contacts 483, for applying ground potential to the control conductor C433. When battery potential is thus removed from the control conductor C433 and ground potential is applied thereto, the trunk 430 is marked as busy to the incoming selectors 434, etc., and to the selectors of the finder-selector links 426, etc., having access thereto; whereby the trunk circuit 400 is marked as busy to the switches mentioned.

Also, upon operating the switch relay R460 completes, at the contacts 463, a path including the contacts 451, for bridging the right-hand winding of the answer relay R445 across the line conductors C436 and C437 of the trunk 435 extending to the incoming selector 429; whereby the incoming selector 429 operates to return ground potential over the control conductor C438 of the trunk 435 in order to energize in multiple the left-hand winding of the answer relay R445 and the lower winding of the switch relay R460. Accordingly, a holding circuit is thus cornpleted for energizing the lower winding ot the switch relay R460; and the left-hand winding of the answer relay R445 is not poled to operate. At this time the incoming selector 429 is conditioned to be responsive to the first digit transmitted thereto over the trunk 435.

The subscriber at the calling subscriber substation T11 in the remote exchange 10 then dials the first digit l of the directory number of the called subscriber substation T21 in the tandem exchange 20; whereby the line relay R330 in the trunk circuit 200 follows the single impulse of the rst digit l restoring and then reoperating. Upon restoring and then reoperating, the line relay R330 interrupts and then recompletes, at the contacts 331, the previously mentioned circuit for maintaining operated the hold relay R380; whereby ther latter relay being of the slow-to-release type, remains operated during impulsing.

Also, upon restoring and then reoperating, the line relay R330 completes and then interrupts, at the contacts 332, a circuit, including the contacts 337, for operating the dial relay R320 in order to cause the latter relay to operate and remain operated during impulsing as it is of the s1ow-torelease type. Upon operating, l the dial relay R320 completes, at the contacts 324, an alternative termination circuit including the contacts 311, the resistor 344, the contacts 281, the condenser 286, and the condensers 347 and 348 across the line conductors C301 and 13 C302 extending to the carrier equipment 394. Also, upon restoring'and lthen .reoperating, the line relay R330 interrupts and then .recompletes, at the contacts 333,'the previouslym'entionedpath'for applying ground potential tothe signal-out conductor C303, 'thereby to cause therv signalout relay R397 'torestore and then to reoperate. Whenlthe signal-out relay`R397 in the carrier equipment 394 restores 'and 'then reoperates, it interrupts and then recomplete's, 'atthe vconta'cts398,the plate circuit of the associated'transmitting amplifier; whereby the 24.55 kc. carrier 'signal is removed from and then reapplied to vthe line "60 extending between "the remote Aexchange 10 and the'tandem exchange 20.

"When 'the 24.5"5 "k'c. carrier 'signal is removed from and 'then reapplied to the "line 60, the signal-in 'relay R495 -inihe carrier equipment 494'disp'osed in the tandem exchange 20 'reoperates .andthenjrestoreg interrupting andthen re'compl'eting, 'atthe contacts 496, the previously mentioned p'ath for applying ground potential to the signal-in conductor C404; 'thereby'to cause the signal-in relay'R450 in vthe 'trunk circuit 400 to restore 'and then reoperate. 'Upon restoring and then reoperating, the signalain relay R450 interrupts and then 'recompletes, 'at the contacts 452, the 'previously mentioned circuit 'for maintaining operated the hold relay R400; whereby the latter relay being ofthe slow-to-release ltype, remains operated during 'impulsing Also, upon 4restoring `and then reope'1ating,tl1e sig'nal-'inrelay R450 completes 'and then interrupts, at -lthe contacts 453, la circuitinclu'ding the contacts 4406 -for operating the dial relay'vR455, thereby "to cause the latter relay 'to operate and remain op'erated'during'impulsing.as it 'is ofithe slow-to-release type. Upon voperating lthe dial relay "R455 completes at the contacts 1457, an obvious path, including theresistor '454, for short-circuiting the right-hand winding of the answer :relay R445.- ,"Fin'ally, .upon vrestoring .and then .upon reoperating the signal-.in relay R450 interrupts and 'then trecompletes, at the contacts 451, the previously 'traced loop circuit including the .line conductors C436 and JC437 of -the .trunk '435 extending lto the incoming selector '429; whereby the single impulse of I'the .rst digit 1 o'f the 'directorynumber of the called subscriber substation T21 is repeatedover'the trunk '435 tothe incoming selector 429. 4The incoming selector 429 responds vto thedigit Yl to select the Vgroup of trunks extending .to the first group of local connectors,`including theloca'l connector '427,and then to .select anidle trunk in Lthegroup mentioned. ,`Forexample,theincoming selector 429 may 'select the trunk'428 extending `to the particular 'local connector 427; whereby thelocal connector -427 .is conditioned tobe responsive to the `next two digits transmitted over 'the trunk 435.

At lthe conclusion of the dialing of the first digitl at the .calling subscriber substation T11 V'in the remote exchange 10, the line rel-ay R330 .in the trunk circuitf200 is-retainedin .its `operated-,position as lpreviously noted; and shortly thereafter the dial relay 'R320 restores, as it is of'the sloW-tofrelease-type. `Upon .restoring the dial relay/.R320 interrupts, .at .the contacts .324, the alternativetermination circuit, .previously traced, across the line conductors C301 and C302 extending to thecarrier equipment .394. Also, at the .conclusion .of the dialing ofthe iirst-.digitl at .the callingsubscriber substation T11 in :the -remote exchange l1.0, :the vsignal-in .relay .R450 .in thetrunk circuit .400 is retained in its operatedpositio-n andshortly .thereafter the dial relay .R455 restores to interrupt .atfthevcontacts' 457, fthe previously traced path, including: the resistor 454, .for .short-circuiting the righthand winding of the lansweimrelay R445; .whereby the rightfhand Winding -of .the `.answer .relay .R455 Vis Yagain energized .in lthe .previously traced :loop circuit including the trunk 435 extending to the .incoming -.selector 429. However, .theanswerrelay R445 is .notpoled to operate at this time.

.At Vthis time -the subscriber at the calling subscriber substation 1211 in the remote exchange 10 has dialed the Aiirs't .digit 'l of `the directory number Aof the called subscriber substation AT21 in the tandem exchange 20; whereby lthe `line relay R330 in the trunk circuit '200 followed .the digit mentioned repeating the same to the carrier equipment 394; the signal-out relay'R397 in the carrier equipment 394 repeated thedig'itmentioned over the line 60 to the carrier equipment 494; .the signal-in relay R495 in the carrier equipment 494 repeated the digit mentioned to .the signal-'inrelay'R450 in .the trunk circuit 400; the signalin relay lR450 repeated the digit mentioned .over .the trunk 435 to the incoming selector 429; and the incoming selector 429 followed the digit mentionedin order to select -the -idle local connector 427 in the corresponding group. `ln a similar manner, the subscriber at the-.calling..subscribersubstation T11 in the remote exchange 10 dials the vsecond and .third digits 2 and l of the directory number of the called subscriber substation T21 in the tandem exchange 20; whereby the two digits .are repeated '.in .the manner previously explained to the local-connector .427. The local connector 427 .responds to thesecond digit 2 of .the director-ynumber of the called subscriber substation T21 in -the .tandem exchange '20 to select `'the corresponding group .of .subscriberlines; .and ythen responds to the third digit l Vof the directory .number ofthe .called vsubscriber substation T21 to .selectthe .subscriber line 421 extending thereto. At this time the.local.connector 427 operates to'testthe idle Aor busy .condition of .the called .subscriber .substation T21 in. accordance .with Iconventional practice.

In the event .the called subscriber substation T21 .is busyatthis time, the line circuit 423 individual to .the subscriber line 421 .extending thereto .has .mmked the condition .noted .to the local connector 427; whereby the local .connector 427 operates tocause busy vtone Vcurrent :to .bereturned over .the trunk 428'andthe incoming selector 429 and overtheline conductors C436 and C437 ofthe trunk 435. At thistime, the line conductor C436 of .the trunk 435 is .connected .by way of the contacts 463, 456and 462 .to the `lineconductor C402 'extending to .the .carrier equipment 494; :and vthe line conductor C437 .of .the trunk 435 is .connectedby way .of .the vcontacts 451 andi-465 to the ,line-conductor C401 extending to the carrier equipment 494. Accordingly, ybusy tone current is .returned-over the above traced path including the lineconductors .C401and vC402 to the carrier equipment 494; `whereby the balancedmodulator therein operates to .transmit-the lower side vband vvof the 15.95 kc. carrier :signal modulatedlby .the yaudio ybusy signal vover the line 60:.extending .between the `tandem exchange 20 andthe remote 'exchange .10. When the lower side band of thc .15.95 kc. carrier signal modulated bythe audio busy'signal 4is .receivedfby the carrier equipment 394 in thezremoteexchange 10, the balanced demodulator thereindernodulates the received signal transmitting the modulating audio busy signal component thereof .over the linewconductors C301 and C302 that are coupled by .way of the previously traced circuit to the line conductors C226 .and C227 of the trunk 225. The audio bus-y signal returned overrthe line conductors C226 andlC227"of.the trunk .225 isreturned over the under-selector link 203.and the .subscriber .line 211 "to rthe calling subscriber substation .Tllinthe l'remoteexchange v10, thereby to indicate tothe subscriber thereat that. the desired connection may 'not behad atvv this time by virtue of the busy condition of .the cal-led subscriber .substation .T21 .in the tandem exchange V20. Thesubscriberat the calling subscriber substation T11 in .the remote exchange `10 then proceeds to .release `the apparatus in a manner more fully explained hereinafter.

Now assuming .that the called subscriber substation T21 in the tandem exchange v20 is idle when -the local connector 427 operates lto 'select the subscriber .line 421 extending thereto, .thelocal connector 427 operates .to project ringiugcurrent over .thesubscriber line 421 ex- 15 tending to the called subscriber substation T21 and to effect operation of the line circuit 423 associated with the subscriber line 421 in order to mark the subscriber line 421 as busy to the other local connectors in the associated group. Also, the local connector 427 returns ring-back tone current over the trunk 42S, the incoming selector 429 and the line conductors C436 and C437 of the trunk 435; which audio ring-back tone current eiects operation of the carrier equipment 494 in the tandem exchange 20 and the carrier equipment 394 in the remote exchange in the manner previously explained; whereby the audio ring-back tone current is returned over the trunk circuit 200, the trunk 225, the finder-selector link 203 and the subscriber line 211 to the calling subscriber substation T11 in the remote exchange 10 in order to indicate to the subscriber thereat that the subscriber at the called subscriber substation T 21 in the tandem exchange 20 is being rung.

When the subscriber at the called subscriber substation T21 in the tandem exchange 20 answers the call, the local connector 427 operates to reverse the polarity of the trunk 428 and, consequently, the polarity of the line conductors C436 and C437 of the trunk 435 over the incoming selector 429; whereby the right-hand winding of the answer relay R445 in the trunk circuit 400 is poled to operate. Upon operating the answer relay R445 interrupts, at the contacts 446, a normally completed termination circuit including the condenser 443, the resistor 444 and the contacts 471 across the line conductors C401 and C402 extending to the carrier equipment 494 and completes, at the contacts 447, an obvious circuit for energizing the upper winding of the supervisory relay R440 in order to cause the latter relay to operate. Upon operating, the supervisory relay R440 completes, at the contacts 442, an obvious path for applying ground potential to the signal-out conductor C403 in order to effect operation of the signal-out relay R497 in the carrier equipment 494. Upon operating the signal-out relay R497 in the carrier equipment 494 closes the contacts 498 included in the plate circuit of the associated transmitting amplifier; whereby the associated carrier frequency oscillator transmits the 15.95 kc. carrier signal over the line 60 extending between the tandem exchange 20 and the remote exchange 10.

When the 15.95 kc. carrier signal is received by the carrier equipment 394 in the remote exchange 10, the apparatus incorporated therein eiects the restoration of the signal-in relay R395 therein. Upon restoring the signalin relay R395 in the carrier equipment 394 completes, at the contacts 396, a path for applying ground potential to the signal-in conductor C304 in order to eiect operation of the signal-in relay R350 in the trunk circuit 200. Upon operating the signal-in relay R350 completes, at the contacts 352, an obvious circuit for operating the hold relay R340. Upon operating, the hold relay R340 completes, at the contacts 341, a circuit including the contacts 385 and 256 for operating shortly thereafter the timer relay R235, the latter relay being of the slowto-operate type. Upon operating the timer relay R235 completes, at the contacts 237, a circuit, including the contacts 352, for operating the reverse battery relay R240. Upon operating the reverse battery relay R240 reverses, at the contacts 241, 242, 243 and 244, the polarity of the line conductors C226 and C227 of the trunk 225 with respect to the upper and lower windings ofthe line relay R330 in the trunk circuit 200. When the polarity of the trunk 225 is thus reversed, the meter, not shown, associated with the calling subscriber line 211 is operated in order to meter the call from the calling subscriber substation T11 in the remote exchange 10 to the called subscriber substation T21 in the tandem exchange 20.

At this time a connection is established between the calling subscriber substation T11 in the remote exchange 10 and the called subscriber substation T21 in the tandem 16 exchange 20. When an audio signal originates at the calling subscriber substation T11, it is transmitted over the previously traced path including the line conductors C301 and C302 to the carrier equipment 394 in the remote exchange 10; whereby the carrier equipment 394 operates to transmit the lower side band of the 24.55 kc. carrier signal (21.7 to 24.3 kc.) over the line 60. When the carrier equipment 494 in the tandem exchange 20 receives the lower side band of the 24.55 kc. carrier signal (21.7 to 24.3 kc.) it operates to transmit the audio compcnent thereof over the previously traced path including the line conductors C401 and C402 to the called subscriber substation T21. Similarly, when an audio signal originates at the called subscriber substation T21, it is transmitted over the previously traced path including the line conductors C401 and C402 to the carrier equipment 494 in the tandem exchange 20; whereby the carrier equipment 494 operates to transmit the lower side band of the 15.95 kc. carrier signal (13.1 to 15.7 kc.) over the line 60. When the carrier equipment 493 in the remote exchange 10 receives the lower side band of the 15.95 kc. carrier signal (13.1 to 15.7 kc.) it operates to transmit the audio component thereof over the previously traced path including the line conductors C301 and C302 to the calling subscriber substation T11.

At the conclusion of the established connection, when the subscriber at the called subscriber substation T21 in the tandem exchange 20 disconnects, the local connector 427 again operates to reverse the polarity over the trunk 428 and the incoming selector 429 to the line conductors C436 and C437 of the trunk 435; whereby the right-hand winding of the answer relay R445 in the trunk circuit 400 is poled to restore. Upon restoring, the answer relay R445 recompletes, at the contacts 446, the previously traced termination circuit across the line conductors C401 and C402 extending to the carrier equipment 494; and interrupts, at the contacts 447, the previously mentioned circuit for energizing the upper winding of the supervisory relay R440 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Upon restoring, the supervisory relay R440 interrupts, at the contacts 442, the previously mentioned path for applying ground potential to the signal-out conductor C403, thereby to effect the restoration of the signal-out relay R497 in the carrier equipment 494. Upon restoring the signal-out relay R497 interrupts, at the contacts 498, the plate circuit of the associated transmitting' amplifier; whereby the 15.95 kc. carrier signal is removed from the line 60. When the 15 .95 kc. carrier signal is thus removed from the line 60, the carrier equipment 394 responds eiecting reoperation of the signal-in relay R395 therein.:

Upon reoperating the signal-in relay R395 in the carrier equipment 394 interrupts, at the contacts 396, the previously mentioned path for applying ground potential to the signal-in conductor C304; thereby to eect the restoration of the signal-in relay R350 in the trunk circuit 200. Upon restoring, they signal-in relay R350 interrupts, at the contacts 352, the previously traced multiple circuits for maintaining operated the hold relay R340 and the reverse battery relay R240; whereby the hold relay R340 being of the slow-to-release type, restores shortly thereafter and the reverse battery relay R240 restores immediately. Upon restoring the reverse battery relay R240 again reverses, at the contacts 241, 242, 243 and 244, the polarity of the trunk 22S with respect to the upper and lower windings of the line relay R330; however, without eiect at this time. Upon restoring the hold relay R340 interrupts, at the contacts 341, the previously traced circuit for maintaining operated the timer relay R235.

When the subscriber at the calling subscriber substation T11 in the remote exchange 10 then disconnects, the previously traced loop circuit for maintaining operated the line relay R330 in the trunk circuit 200 is interrupted. Upon restoring, the line relay R330 interrupts, at the contacts 331, the previously traced circuit for maintaining anale@ operated the hold relay R380 in order to cause the latter relay to restore shortly thereafter, it being of the slow-v to-release type. Also, upon restoring the line relay R330 interrupts, at the contacts 333, the previously mentionedv path for applying ground potential to the signal-out conductor C303, thereby to eiect the restoration of the signalout relay R397 in the carrier equipment 394. Upon restoring, the hold relay R380 recompletes at the contacts 381, the previously traced termination circuit including the resistor 344 and the condenser 286 as well as the condensers 347 and 348 across the line conductors C301 and C302 extending tothe carrier equipment 394; and interrupts, at the contacts 384, the previously traced path for applying ground potential by way of the upper winding of the tone relay R390 to the control conductor C223 lof the trunk 225; and recompletes, at the contacts' 383, the previously traced path for applying battery potentialv by way of the impedance 257 to the control conductor C223 of the trunk 225 in order to cause the vtone relay R390v to restore. When ground potential is thus removed from the control conductor C223 of the trunk 225 a-nd battery potential is reconnected thereto, the finder-selector link 203 is released and the trunk 225 is marked as idle to the selectors of the iinder-selector links 203, etc., having access thereto. When the finder-selector link 203 is thus released, the line circuit 213 operates in order to mark the subscriber line 211 extending to the subscriber substation T11 as idle to the local connectors 205, et'c., having access thereto.

When the signal-out relay R397 in the carrier equipment 394 restores, it interrupts, at the contacts 398, the plate circuit of the associated transmitting amplifier; whereby the 24.55 kc. carrier signal is thus removed from the line 60. When the 24.55 kc. carrier signal is thus removed from the line 60, the carrier equipment 494 responds, effecting reop'eration of the signal-in relay R495 therein.

Upon reoperating, the signal-in relay R495 in thel carrier equipment 494 interrupts, at the contacts 496, thev previously mentioned path for applying groundE potential tothe signal-in conductor C404; thereby to eect restoration of the signal-in relay R450 in the trunk circuit 400. Upon restoring the signal-in relay R450 interrupts, at the contacts 451, the previously traced loop circuit extending between the right-hand winding of the answerv relay R445'- and the trunk 435; whereby the local connector 427'y and the incoming selector 429' included in this loop circuit are released. When the local connector 427 is thus released the line circuit 423 is operated in order to mark the subscriber line 421 extending to the subscriber substation T21 as idle to the local connectors 427, etc., having access thereto. When the incoming selector 4-29 is thus released, the trunk 428 extending to the local connector 427 is marked as idle to the incoming selectors 429, etc., having access thereto. Also, when the incoming selector 429 is thus released, ground potential therein is removed from the control conductor C438 ofthe trunk 43'5, thereby to interrupt the previously traced multiple circuits for yenergizing the left-hand winding of the answer relay R445 and the lower winding of the switch relay R460. Also, upon restoring, the signal-in relay R450 interrupts, atA the contacts 452, the previously traced circuitV for maintaining operated the hold relay R400; whereby the latter relayv restores shortly thereafter, it being of the slow-to-release type. Upon restoring the holdvrelayl R400'interrupts, at the contacts 405, the previously traced circuit for energizing the upper winding ofthe switch relay R460 in* order to cause the latter relay tol restore. Upon restoring-.the switch relay R460 interrupts, at the contactsi 467, the previously traced path for applying ground: potent-iaE to the control conductor C433 of the trunk 430 and'* recompletes, at the contacts 466, the previously traced path for applying battery potential by way of the impedancc'458t'o the control conductor C433; whereby theI trunk 430- is marked as idle to the incoming selectors 434, etc., and to the selectors of the finder-selector links 426, etc., having access thereto.

At this time, the established connection between the calling' subscriber substation T11 in the remote exchange 10 and the called subscriber substation T21 in the tandem exchange 20 is released and all of the apparatus involved therein is completely released and available for further use.

In view of the foregoing, it will be understood that a connection may be extended from a calling subscriber substation. T11, etc., in the remote exchangey 10 to a `called paystation T22, etc., in the tandem exchange 20 lin `an identical manner. Also, it will be understood that a connection from a calling paystation T12, etc., in the remote exchange 10 may be extended to a called subscriber substation T21, etc., or toa called paystation T22, etc., in the tandem exchangek 20 in a substantially identical manner. In this conjunction, it is noted incident to extending a connection from the calling paystation T12 in the remote exchange 10 to a called subscriber substation or toa called paystation in the tandem exchange 20, that when the call is answered, the apparatus operates in order to eifect operation of the reverse battery relay R240 in the trunk circuit 200; whereby the polarity of the trunk 225 isv reversed with respect to the 'upper and lower windings of the line relay R330 in the trunk circuit 200; all in the manner previously explained. This reversal of polarity over the trunk 225 and over a linderselector link such, for example, as the finder-selector link 203 and the'liue 212 extending to the paystation T12 brings about blocking. of the transmitter at the paystation T12 by theA associated copper oxide rectifier, unless the person at the paystation. T12 has deposited a coin at this time. More particularly, in the event the person at the calling paystation T12 `has not depositeda coin at this time, he may hear the person at the called subscriber substation or at the called paystation in the tandem exchange 20, but he may not talk to the person mentioned by virtue of the circumstance that the copper oxide rectier blocks the associated transmitter as a consequence of the reversal of the polarity to the calling paystation T12. However, when the person at the calling paystation T12 deposits a coin, the copper oxide rectifier is removed from blocking the transmitter thereat; whereby the connection is completed in the manner previously explained.

A call from a subscriber substation or paystation in the remote exchange 10 to the operator switchboard in the main ofce 40 First assume that a call initiated at a subscriber substation, such for example, as the subscriber substation T11 in the remote exchange 10l is tov be extended to the operator switchboard. 765- in the main otiice 40. Now assume that the finder of the nder-selector link 203 has operated to seize the subscriber line 211' extending to link 203 responds to select anassociated group of trunks,

including the trunk 22:0', and then to select an idle trunk in the group mentioned. For example, ther selector of the hurler-selector link 203 may select the particular trunk 220 extending to the trunk circuit 200; the' trunk 200 being marked as idle by thel application of battery potential by way of the' previously` traced path; includingv the impedance 257,r to the control conductor C223 thereof. Aigo, when. they senatorof the ander-senator linkv i 203 seizes the trunk 220; a loop circuit is completed for'` energizing' in series`v the upper and lower windings of the 

